1. Field of the Invention
The invention relates generally to external bone fixation devices and more particularly to a modular fixation pin for use with an external bone fixation device.
2. Prior Art
External bone fixation devices are well known in the art of orthopedic surgery. Lichty, in U.S. Pat. No. 4,456,005, discloses an external fixation device for compressing a fracture wherein screws are anchored within the fractured bone proximally and distally to the fracture site and the screws are drawn together to promote healing. The screws are percutaneously removed following healing of the fracture. Other similar external bone fixation devices that are exemplary of the state of the art are disclosed in U.S. Pat. Nos. 4,554,915, 4,620,533, 4,919,119, 5,160,335 and 5,314,426.
External bone fixation devices are widely used in orthopedic and reconstructive surgical procedures such as the minimally invasive unification of fractured bones and distraction osteogenesis. Such external bone fixation devices, in operation, essentially include a frame having a plurality of adjustable pin attachment means thereon, and two or more bone fixation pins. The fixation pins are metallic shafts having a threaded, self-tapping invasive distal end adapted to be anchored within a bone, and a non-invasive proximal end adapted to be attached to the frame. The relative positions of the pin attachment means on the frame are adjusted to control the relative positions of the bone segments to which the respective fixation pins are anchored. When the bone segments have been manipulated and positioned as desired, the pin attachment means are immobilized until it is necessary to reposition the bone segments or to remove the fixation pins from the bone.
In accordance with the prior art, in order to implant the distal invasive end of a fixation pin within a bone, the bone is accessed by surgical means and a hole is drilled into an exposed surface of the bone. The threaded, self-tapping distal end of a metallic fixation pin is inserted into the hole, and screwed thereinto until firmly anchored. The opposing (proximal) end of the fixation pin is attached to an external frame via pin attachment means, such as a clamp, that is adjustably connected to the frame. The process is repeated for each fixation pin until the requisite fixation pins are anchored in bone and attached to the frame. The pins are explanted and frame and pins are removed once the therapeutic objective has been achieved.
As will be readily appreciated by those skilled in the art, the self-tapping threads, machined on the distal end of bone fixation pins in accordance with the prior art, are sharp in order to avoid cracking the bone during insertion of the pin thereinto. After the invasive end of such prior art fixation pins are implanted within a bone, the surrounding, sometimes inflamed, soft tissue closes in around the shaft of the pin and is in intimate contact therewith. When the fixation pin is percutaneously explanted, counterclockwise rotation of the pin is required in order to back the pin out of the hole. During pin removal, the sharp, metallic, self-tapping threads on the pin may cause damage to delicate surrounding tissue structures such as vascular and nerve tissue. There remains a need for a bone fixation pin which minimizes damage to tissue when removed from a bone.
It is a first object of the invention to provide a fixation pin for use with an external bone fixation device wherein when the fixation pin is percutaneously removed from a bone, the damage to tissue adjacent the fixation pin is minimized.
It is a second object of the invention to provide a bone fixation pin meeting the first objective which can be used with a variety of currently available bone fixation frames for performing a variety of procedures requiring the use of a bone fixation device.
It is yet another object of the invention to provide a hybrid bone fixation pin meeting the above objectives, at least a portion of which is biodegradable.
The features of the invention believed to be novel are set forth with particularity in the appended claims. However, the invention itself, both as to organization and method of operation, together with further objects and advantages thereof may be best understood by reference to the following description taken in conjunction with the accompanying drawings in which: